Storm Prediction Center
The Storm Prediction Center ( German storm prediction center ) of the United States in Norman (Oklahoma) is one of the National Centers for Environmental Prediction . It is under the control of the National Weather Service , a division of the National Oceanic and Atmospheric Administration of the US Department of Commerce . Until October 1995, the Storm Prediction Center was located in Kansas City (Missouri) under the name National Severe Storms Forecast Center .
The Storm Prediction Center is responsible for identifying, describing and evaluating the risks posed by convective storms. These risks include tornadoes , hailstones with a diameter of more than 2 cm and winds with speeds of at least 93 km / h. Another task of the Storm Prediction Center is to warn of areas at risk of fire or heavy snowfall. The tasks are essentially followed by convective outlooks , severe thunderstorm watches and tornado watches , weather watches and mesoscale discussions . In a three-stage process, the area, the time span and the details of a weather warning are continuously specified and attention is increased in the process.
Convective outlooks
The Storm Prediction Center forecasts the general threat of conective storms in the United States for the next 6-73 hours and divides the risks into three categories. There is a separate forecast for each of the coming days, which is updated up to five times a day.
Categories
The categories are ordinary storms (only with a short description), "SEE TEXT" (an area on the map of isolated storms or severe weather-like conditions), "SLGT" (low risk), "MDT" (moderate risk), and "HIGH "(great dangers).
Endangered areas (shown in hatched areas on the map) indicate a major threat. This includes tornadoes from strength F2 , hailstones with a diameter of at least 5 cm or storms with a speed of more than 120 km / h. Public severe weather warnings are issued when severe or widespread severe weather is anticipated, especially in the event of tornadoes.
A Low Hazard Day (SLGT) indicates isolated hazards from strong winds, heavy hail or local tornadoes. During the storm season, there is little danger for individual areas of the United States on most days.
Moderate Hazard Days (MDT) warn of more widespread and more dangerous storms. These can include numerous tornadoes with higher wind speeds, more widespread areas with strong winds, or hail showers with very large hailstones. On a few days with moderate dangers, strong tornadoes or derechos occur . Such warnings are not uncommon and are issued several times a month during the high season.
A Day of Great Hazards (HIGH) has a significant chance of a large tornado or an exceptional derecho occurring. On such days there is a risk of extreme storms with life-threatening effects from widespread strong or very strong tornadoes and / or other destructive winds. Hail alone cannot trigger the highest warning level. Many of the days of greatest devastation were those with great dangers predicted. These usually only happen a few times a year.
It should be noted that the categories are only predictions and do not always apply. In the past, for example, stronger tornadoes occurred on days with little danger and a lack of great danger is not uncommon.
The predictions
The forecast for one day is updated five times a day. At 06:00 UTC , the first forecast is made for the time from 12:00 UTC on the current day to 12:00 UTC the following day. Updates are made at 13:00 UTC, 16:30 UTC, 20:00 UTC and 01:00 UTC and affect the remaining period up to 12:00 UTC. The prediction consists of a text, a card with categories and probability of occurrence and a diagram of the probabilities. The one-day forecast is the only one that provides concrete probabilities for tornadoes, hail and strong winds. Of all the forecasts, it is the one with the most detailed forecasts and the highest accuracy.
The forecast for two days is published daily at 08:00 UTC and 17:30 UTC and is valid for 24 hours from 12:00 UTC on the following day. It contains only a basic estimate with a text and a diagram of the general probability of severe weather. It is very unusual for a two-day forecast to warn of moderate danger. A warning of major dangers has only been issued on April 7, 2006.
The three-day forecast includes the same outputs as the two-day forecast. As accurate forecasts become more difficult as time goes on, higher category warnings three days in advance are rare. A three-day forecast warned of moderate dangers only five times (June 10, 2005, January 2, 2006, April 24, 2007, June 6, 2007 and July 7, 2007). So far there has been no warning of great danger.
The forecasts for four to eight days mainly consist of texts and can change completely within a day, as an accurate forecast over such a long period is not possible today reliably. Maps only show areas with a risk of at least 30% and are rarely used due to the difficulty of forecasting. The longer-term predictions were in the experimental stage until March 22, 2007. Since then, they have been part of the official predictions.
Local National Weather Service, radio and television stations, and contingency planners often use the forecasts to assess the threats to their area.
The following table shows the warnings issued depending on the type of storm or the duration until it occurs, as well as the probability of occurrence within a 40 km radius. (H = hatched area; the 2% and 10% probabilities are only used for tornadoes.)
| tornado | wind | hail | Day 2/3 | |
| 2% | SEE TEXT | |||
| 5% | SLGT | SEE TEXT | SEE TEXT | SEE TEXT¹ |
| 10% | SLGT | |||
| 15% | MDT | SLGT | SLGT | SLGT |
| 30% | HIGH | SLGT | SLGT | SLGT |
| 45% | HIGH | MDT | SLGT | SLGT |
| 45% (H) | HIGH | MDT | MDT | MDT |
| 60% | HIGH | MDT | MDT | MDT² |
| 60% (H) | HIGH | HIGH | MDT | HIGH² |
¹Warning can be at SLGT level if there is only a risk of tornadoes (this is usually the result of a tropical cyclone ).
² Warning will not be issued for day 3.
